A new micromethod for the rapid, reliable fractionation of plasma lipoproteins, and quantitation of their cholesterol content has been developed. This method requires 350 microliters of plasma, and can be completed in 3 hours. This method should facilitate the measurement of cholesterol in lipoprotein fractions by routine clinical laboratories. Techniques for the quantitation of apolipoproteins are under development. Measurements of apoA, C, D, E, and B have been completed in 6 patients with Tangier disease, and indicate a heterogeneity of apolipoprotein levels. These results are consistent with the possibility that patients with Tangier disease may have different metabolic defects.